TORONTO - When a child dies, it's a tragedy. When a parent or someone else is mistakenly accused of the child's death, or a killer goes free on shoddy evidence, a tragedy becomes horribly compounded.

That's the backdrop to public inquiry hearings beginning Monday in which the science of pediatric forensic pathology will be placed under a judicial microscope.

Led by Justice Stephen Goudge, the inquiry was called after an expert panel questioned the findings of pathologist Dr. Charles Smith, once regarded as the dean of his field in Canada, in 20 of 45 child death cases he handled going back to 1991.

Criminal proceedings resulted in 13 of those cases.

At the intersection of Smith's renown as the country's leading pediatric forensic expert and the criminal justice system are heart-rending cases of dead babies and children, and the men and women believed to have been wrongfully denounced as their killers.

Some of those cases have gained widespread notoriety.

William Mullins-Johnson, for example, spent 12 years in prison for killing his four-year-old niece in 1993 near Sault Ste. Marie, Ont., before his conviction was quashed this past summer.

Smith, who once said he had "a thing against people who hurt children,'' testified Valin had been anally raped and suffocated, a finding several other experts would later argue was a terribly misguided analysis with zero forensic evidence to support it.

He also concluded that Louise, 28, used scissors to stab her seven-year-old daughter, Sharon, more than 80 times in 1997. Louise spent more than three years in custody before another expert pinned Sharon's death on a pit bull and the charges were dropped.

"I expect the families will be able to get some answers about mistakes that were made in the past,'' said Louise's lawyer, Peter Wardle, who represents several parties at the inquiry.

On Thursday, the Supreme Court of Canada ordered a new trial for Marco and Anisa Trotta, convicted of beating their eight-month-old baby Paulo to death in 1993. He spent nine years in jail before winning bail in May; she served a five-year term.

Goudge has met privately with 20 people, either those accused or otherwise directly connected to cases, and also quietly visited two First Nations reserves in northern Ontario this summer.

The inquiry, however, will steer clear of finding legal fault.

"It is not a trial -- criminal or civil -- and I cannot make findings of criminal or civil liability,'' Goudge, who sits on Ontario's Court of Appeal, said in June.

That doesn't mean the cases that underpin the inquiry won't get a thorough airing.

"We really do have to know some level of detail about what happened and why,'' said Linda Rothstein, the inquiry's lead lawyer.

"We're not going to conduct a systemic inquiry in a factual vacuum. That wouldn't be helpful to anyone. We do have to anchor the commissioner's recommendations in what really did happen.''

Most of the hearings, which will take about three months, will comprise a broader look at the practice of pediatric forensic pathology, with a view towards restoring battered confidence in a branch of medicine where oversight appears to have fallen through the cracks.

Among the issues at play is the relationship between police, pathologists and Crown prosecutors, and what all too often turns out to be a mistaken, single-minded approach that focuses on a single suspect.

"Definitely, tunnel vision is one of the issues the inquiry will be looking at,'' Wardle said.

One thread running through several cases is the socio-economic status of each accused -- minorities, aboriginals or single mothers, some of whom hid their pregnancies -- and whether the criminal justice system they got caught up in was stacked against them from the get-go.

Smith, who exudes an air of self-confident expertise, has faced fierce criticism over the years from judges, defence lawyers and those his evidence has convicted, as well as what his lawyers describe as "highly adverse'' and "highly prejudicial'' media coverage.

Smith himself is due to testify at the end of January and will pay his own legal freight for the inquiry. He has refused a pre-interview by commission lawyers. His lawyers did not respond to several requests for an interview.

Grisly autopsy photographs are among the items to be presented as evidence, but they will be kept out of the public eye out of respect for the subjects and their relatives, said Rothstein.

There are also photographs of Smith's office -- described in ghoulish terms by those familiar with the apparently disorganized assortment of organs, skulls and other body parts -- at the Hospital for Sick Children in Toronto from where he acted as an independent expert Crown witness.

"Experts in a courtroom -- we give great deference to experts. That's the history of the problems,'' said Bill Trudell, chairman of the Canadian Council of Criminal Defence Lawyers.

"The Goudge inquiry will change that and start people thinking that these experts are human and can make mistakes.''

When it comes to pathology, however, the work is both complicated and nasty. Glamour treatment given by popular American television dramas such as "CSI'' have created unrealistic expectations as well.

"What we're going to hear from forensic pathologists is that the `CSI' effect has been unfortunate,'' Rothstein said.

"The notion that there can be that level of uncertainty about most, if not all, of their conclusions, is unfortunate.''

Due to testify later this month is Dr. James Young, who was Ontario's chief coroner.

Young is expected to face questions about the oversight of pathologists and the handling of numerous complaints about Smith over the years, as is the College of Physicians and Surgeons of Ontario.

One complaint was made by Brenda Waudby, of Peterborough, Ont., whose charge of murdering her two-year-old daughter Jenna was eventually dropped. She maintains that Smith kept a hair that might have identified the killer -- found during an autopsy -- in a drawer for five years.

Dr. Barry McLellan, also former chief coroner of Ontario, and Dr. Michael Pollanen, Ontario's chief forensic pathologist, are due to testify as members of an expert panel this week.

"My biggest surprise is how extraordinarily difficult it is to do the work of forensic pathology,'' Rothstein said.

"There are not too many people who line up to do it. We're asking an awful lot of those people.''

The inquiry, with six lawyers assisting Goudge, is tapping experts both in Canada and internationally.

The hearings are expected to wrap up by March 1, with Goudge due to report to Ontario's attorney general by April 25.